Numerous attempts have been made to harness water flow as a source of energy. Horizontal axis water mills were one of the first means of powering industrial machinery. Undershot and overshot wheels have been employed for centuries. Historic screw type turbines have been invented also. Such early designs lacked efficiency and reliability.
Reaction turbines, such as a Pelton wheels, which employ a jet or jets of water have been used to improve efficiency. Impulse wheels, such as Francis and Kaplan wheels have also been produced, with further improved efficiency. These impulse wheels generally have an enclosed bladed turbine set of various geometries. However these designs rely on complex sets of turbine blades and complementary curved/scrolled housings, which are expensive to manufacture, and not easy to repair because they are enclosed. Where it is impracticable to capture water flows in pipes and the like, for example in tidal sea flows, such reaction and impulse type designs are impracticable. Francis rotors and Kaplan rotors are examples of turbine rotors that rotate about an axis that is aligned with the overall direction of the fluid flowing through them. Savonius rotors and Darrieus rotors are examples of turbine rotors that rotate about an axis that is transverse with the overall direction of the fluid flowing through them, but which do not necessarily require enclosure. Embodiments of this invention relate to these latter turbines, which are also called vertical axis turbines or cross axis turbines.
Where tidal flows are harnessed, it is quite possible that for some of the time, only a part of the turbine will be submerged, and the flow will reverse with the rise and ebb of the tide. So enclosed turbines will be of no use, unless a significant superstructure is constructed to channel water flow at most stages of a tide. One example of such a superstructure is disclosed in GB2495443 which shows a vertical/cross axis turbine arrangement combined with a barrage and water channels.
Various other vertical axis tidal flow turbines have been considered, without the need for such a superstructure but these known designs are weak and/or complicated. Such designs are disclosed, for example in CA2849054; KR20130096060; and WO2013030582.
Where turbines are intended for commercial use in remote or inaccessible areas, such as deep under water or in strong tidal flows, then low cost, ease of installation, and reliability, are the most important factors. Efficiency is important but is secondary. So a water channelling superstructure is too expensive in most cases, unless they have another use, such as a water dam or a vehicle bridge. Enclosed turbines are also expensive and difficult to repair, particularly under water.
The inventors have realised that a simple and strong, self-contained design can mitigate some of the drawbacks of previous designs, and propose herein, embodiments which address those drawbacks.
The invention provides a water flow turbine arrangement for capturing energy from the water flow according to the independent claims herein having preferred features defined by dependent claims.
The invention extends to any combination of features disclosed herein, whether or not such a combination is mentioned explicitly herein. Further, where two or more features are mentioned in combination, it is intended that such features may be claimed separately without extending the scope of the invention.